Internet-Draft Analysis of metric distribution March 2023
Shi Expires 14 September 2023 [Page]
Intended Status:
H. Shi
Huawei Technologies

Design analysis of methods for distributing the computing metric


This document analyses different methods for distributing the computing metric from the service instance to the ingress router.

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This Internet-Draft will expire on 14 September 2023.

1. Introduction

Many modern computing services are deployed in a distributed way. Multiple service instances deployed in multiple sites provide equivalent function to the end user. As described in [I-D.yao-cats-ps-usecases], traffic steering that takes computing resource metrics into account would improve the quality of service. Such computing metrics are defined in [I-D.du-cats-computing-modeling-description]. This document analysis different methods for distributing these metrics.

2. Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

This document uses terms defined in [I-D.ldbc-cats-framework]. We list them below for clarification.

  • Computing-Aware Traffic Steering (CATS): An architecture that takes into account the dynamic nature of computing resources and network state to steer service traffic to a service instance. This dynamicity is expressed by means of relevant metrics.
  • CATS Service Metric Agent (C-SMA):Responsible for collecting service capabilities and status, and reporting them to a CATS Path Selector (C-PS).
  • CATS Path Selector (C-PS): An entity that determines the path toward the appropriate service location and service instances to meet a service demand given the service status and network status information.

3. Requirement of distributing computing metric

The function components of the CATS is defined in [I-D.ldbc-cats-framework](see Figure 1, the figure is replicated here for better understanding). C-SMA is responsible for collecting the computing metric of the service instance and distributing the metrics to the C-PS. C-PS then select the path based on the computing metric and network metric.

      +-----+              +------+            +------+
    +------+|            +------+ |          +------+ |
    |client|+            |client|-+          |client|-+
    +------+             +------+            +------+
        |                    |                   |
        |   +-------------+  |            +-------------+
        +---|    C-TC     |---+     +------|    C-TC     |
            |-------------|         |      |-------------|
            |     | C-PS  |     +------+   |CATS-Router 4|
    ........|     +-------|.....| C-PS |...|             |...
    :       |CATS-Router 2|     |      |   |             |  .
    :       +-------------+     +------+   +-------------+  :
    :                                                       :
    :                                            +-------+  :
    :                         Underlay           | C-NMA |  :
    :                      Infrastructure        +-------+  :
    :                                                       :
    :                                                       :
    :   +-------------+                 +-------------+     :
    :   |CATS-Router 1|  +-------+      |CATS-Router 3|     :
    :...|             |..| C-SMA |.... .|             |.....:
        +-------------+  +-------+      +-------------+
                |         |             |    C-SMA    |
                |         |             +-------------+
                |         |                     |
                |         |                     |
              +------------+               +------------+
            +------------+ |             +------------+ |
            |  service   | |             |  service   | |
            |  instance  |-+             |  instance  |-+
            +------------+               +------------+

              edge site 1                   edge site 2
Figure 1: CATS Functional Components

4. Option 1: Centralized C-SMA + Centralized C-PS

The computing metric can be collected internally by a centralized cloud monitor of the cloud platform. Various tools such as Prometheus for this purpose. The cloud monitor can pass the metric to the network controller. Then the network controller calculate the optimal path and distribute the path to the CATS ingress router. The ingress router just need to steer the flow to the path. The network controller distributed the metric update to the C-PS using south-bound protocol.

5. Option 2: Centralized C-SMA + Distributed C-PS

Similar to option 1, the network controller does not calculate the path. It just passes the computing metric received from the cloud monitor to the C-PS in the CATS ingress router. The C-PS at each CATS ingress router will calculate the best path independently.

6. Option 3: Distributed C-SMA + Centralized C-PS

The C-SMA can be deployed in a distributed way. For example, C-SMA running at each site collects the computing metric of the service instance running in the site. Then it reports the metric to the network controller. The network controller calculates the best path and distribute the path to the CATS ingress router.

7. Option 4: Distributed C-SMA + Distributed C-PS

Similar to option 3, each C-SMA collect the computing metric of each site. Then it needs to distribute the metric to C-PS at each ingress router. It can do so directly or through a network controller.

8. Comparison

Table 1: Comparison between different option
  Option 1 Option 2 Option 3 Option 4
Protocol None Southbound Southbound Southbound or Eastbound
CATS router requirement Low High Low High
Network controller requirement High Low High Low

10. IANA Considerations

This document has no IANA actions.

11. References

11.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.

11.2. Informative References

Du, Z., Fu, Y., Li, C., and D. Huang, "Computing Information Description in Computing-Aware Traffic Steering", Work in Progress, Internet-Draft, draft-du-cats-computing-modeling-description-00, , <>.
Li, C., Du, Z., Boucadair, M., Contreras, L. M., Drake, J., Huang, D., and G. S. Mishra, "A Framework for Computing-Aware Traffic Steering (CATS)", Work in Progress, Internet-Draft, draft-ldbc-cats-framework-01, , <>.
Yao, K., Eardley, P., Trossen, D., Boucadair, M., Contreras, L. M., Li, C., Li, Y., and P. Liu, "Computing-Aware Traffic Steering (CATS) Problem Statement and Use Cases", Work in Progress, Internet-Draft, draft-yao-cats-ps-usecases-00, , <>.


The author would like to thank Xia Chen, Guofeng Qian, Haibo Wang for their help.

Author's Address

Hang Shi
Huawei Technologies